Polysulfones are manufactured by the carboxylicacid anhydride xe2x80x9cpromotedxe2x80x9d reaction of sulfuric acid or sulfur trioxide with an electron rich aromatic compound which behaves as a difunctional (bireactive) compound.
Polysuifones, especially aromatic polysulfones, are important engineering polymers, often having the advantages of chemical resistance, good high temperature properties, good tensile properties, and others. Typical engineering polysulfones are 
Polysulfones may be mad e using Friedel-Craots chemistry. For example, (I) is prepared by reacting 4-biphenylsulfonylchroride with a strong Lewis acid such as aluminum chloride or iron trichloroide. This method has the disadvantage of requiring stoichometric amounts of the Lewis acid catalyst. This catalyst must be removed from the polymer and be discarded or otherwise used. Alternately, polysulfones may be prepared by nucleophilic aromatic substitution chemistry. For example, (II) may be prepared by the homopolymerization of 4-chloro-4xe2x80x2-hydroxydiphenylsulfone, while (III) may be prepared by reaction of the disodium salt of bisphenol A with 4,4xe2x80x2-dichlorodiphenylsulfone. The primary disadvantage of this route is the high cost of the chloride-containing monomers. In addition, production of chloride byproducts which must be properly disposed of is also a drawback of the method.
Reported herein is a method which avoids the drawbacks of the methods described above. In this method, sulfuric acid or sulfur trioxide is reacted with a carboxylic acid anhydride to produce a bisacylsulfate, referred to hereinafter as BAS. BAS is a dielectrophile, that is, it can react twice with nucleophilic compounds. The nucleophile may be an aromatic compound which preferably is electron rich. Use of a nucleophile which can only react once will produce an aromatic sulfonic acid or a diaryl sulfone, depending on the ratio of BAS to nucleophilic aromatic compound used. See for example T. E. Tyobeka, et al., J.C.S., Chem. Comm. 1980, p. 114-115, and R. A. Hancock, et al., J. Chem. Research (S), 1980, p. 270-271. As described herein, if an aromatic nucleophile which can react twice is used it will result in a polysulfone polymer if a 1:1 ratio of the dinucleophile and BAS is used. The byproduct of the reaction is the corresponding carboxylic acid of the carboxylic anhydride. The byproduct acid may be converted back to the original anhydride which then may be recycled back into the process.
This invention concerns, a process for the production of polysulfones, comprising, contacting an aromatic compound which is bireactive, one or both of sulfuric acid and sulfur trioxide, and a carboxylic acid anhydride.
By hydrocarbyl herein is meant a univalent radical containing carbon and hydrogen, while substituted hydrocarbyl means hydrocarbyl substituted with one or more functional groups (including complete replacement of the hydrogens). By hydrocarbylene is meant a divalent group containing only carbon and hydrogen containing two free valences to different carbon atoms. By hydrocarbylidene is meant a groups containing carbon and hydrogen with two free valences to the same carbon atoms, each of these valences bound to a different atom. By substituted hydrocarbylene is meant a hydrocarbylene group substituted with one or more functional groups, and in which all of the hydrogens may be replaced. It is preferred that all of these groups have 1 to 30 carbon atoms.
By a xe2x80x9cbireactivexe2x80x9d compound herein is meant a compound, such as an aromatic compound, in which substantially all molecules of that compound will each react twice in the sulfone forming polymerization process. Since normally the xe2x80x9creactive groupxe2x80x9d in such a compound is a hydrogen bound to a carbon atom, which is not usually thought of as a functional group, the term bireactive is used. If it is unknown whether a particular compound is bireactive a simple test reaction with a model compound under the appropriate reaction conditions will determine whether it is bireactive.
By an xe2x80x9caromatic compound which is bireactivexe2x80x9d is meant a compound which contains at least one aromatic ring, and which is bireactive. This compound may contain more than one aromatic ring. If more than one aromatic ring is present it may be a fused ring system such as found in naphthalene or anthracene, a ring system connected directly by a covalent bond, such as is found in biphenyl, or a ring system connected through another group, such as is found in diphenyl ether, diphenylmethane, and 2,2-diphenylpropane. Other groups may be present on the aromatic rings so long as they do not interfere with the sulfone forming polymerization reaction. It is preferred that the aromatic rings are carbocyclic rings. It is also preferred that the aromatic ring or rings of this compound are naphthyl ring systems or phenyl ring(s), more preferably phenyl rings.
T. E. Tyobeka, et al., Tetrahedron 1988, 44(7), p. 1971-1978 postulate that the sulfone forming reaction is an electrophilic attack on an aromatic ring of the bireactive compound. It is well known in the art that in such electrophilic reactions a substrate, such as the bireactive compound, is more reactive the more xe2x80x9celectron-richxe2x80x9d it is. Aromatic rings can be made more electron rich by having electron donating substituents attached to these rings. Such substituents include groups such as ether, alkyl, and tertiary amino, and are well known in the art. The presence of such groups will tend to make the bireactive compounds more reactive and ensure that it is in fact bireactive instead of monoreactive. Useful compounds for the bireactive compound include naphthalene, methylnaphthalene, methoxynaphthalene, benzyl ether, stilbene, diphenyl carbonate, benzyl phenyl ether, biphenyl, and a compound of the formula 
wherein R1 isxe2x80x94Oxe2x80x94(diphenyl ether), alkylidene (for example xe2x80x94CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94, or (CH3)2C less than ), and R3 is hydrocarbylene, substituted hydrocarbylene or hydrocarbylidene, more preferably alkylene or alkylidene. Preferred bifunctional compounds are (IV), especially when (IV) is diphenyl ether. Useful groups for R3 include 1,2-ethylene, 1,3-phenylene and 1,4-phenylene. More than one bireactive aromatic compound may be present to give a copolysulfone.
Any carboxylic acid anhydride may be used. Carboxylic acid anhydride here has the usual meaning, a compound of the formula R2C(O)O(O)CR2 wherein each R2 is independently hydrocarbyl or substituted hydrocarbyl. It is preferred that both of R2 are the same. It is preferred that Hammett "sgr"m for each of R2 is about 0.2 or more, more preferably 0.4 or more. Hammett "sgr"m constants are well known in the art, see for instance C. Hansch, et al., Chem. Rev., vol. 91, p. 185ff (1991). Preferred groups for R2 are perfluoroalkyl, and perfluoromethyl is especially preferred.
Sulfuric acid and/or sulfur trioxide may be used as the xe2x80x9csourcexe2x80x9d of the sulfonyl group. Particularly if sulfur trioxide is used, it may also be used to form the carboxylic acid anhydride present by dehydration of the corresponding carboxylic acid.
The molar ratio of the aromatic compound which is bireactive to the total of sulfuric acid and sulfur trioxide should preferably be about 1:1, and more preferably about 1.0:1.0, and especially preferably about 1.00:1.00, to achieve higher molecular weight polymer. This is a usual ratio for most condensation polymerizations to achieve higher molecular weight polymer. The molar ratio of carboxylic acid anhydride to sulfuric acid is preferably at least about 2:1, more preferably about 2:1 to about 4:1. The molar ratio of carboxylic acid anhydride to sulfur trioxide is at least about 1:1, preferably about 1:1 to about 2:1. The molar ratios of carboxylic acid anhydride to sulfuric acid and carboxylic acid anhydride to sulfur trioxide are not critical, but these preferred ratios make the most efficient use of the reagents.
The pressure at which the process is run is not critical, autogenous (for processes in which the boiling point of one or more of the reactants is exceeded) or atmospheric pressure being useful. In order to prevent unwanted side reactions such as hydrolysis of the carboxylic acid anhydride by atmospheric moisture, it is convenient to run the reaction under an inert atmosphere, such as nitrogen. The process may be agitated. A useful reaction temperature range is about 0xc2x0 C. to about 300xc2x0 C., preferably about 25xc2x0 C. to about 250xc2x0 C., more preferably about 30xc2x0 C. to about 200xc2x0 C.
The reaction may be run neat, i.e., without other added liquids or solids. It may also be run in the presence of another liquid. This liquid, which should be inert under reaction conditions, may be a solvent for one or more of the starting materials and/or product polymer, but one or more of the process ingredients may simply be suspended in the liquid. Suitable liquids includes alkanes such as octane, electron deficient aromatic compounds such as o-dichlorobenzene, nitroalkanes such as nitromethane, and halogenated alkanes such as 1,2-dichloro-ethane. The process may be run as a batch, semi-batch or continuous reaction. For example a continuous reaction may be run in a continuous stirred tank reactor or a pipeline-type reactor. Such reaction systems are well known in the art.
Aromatic compounds that are trireactive or higher may also be present in the process in small amounts (to produce a thermoplastic). Addition of these xe2x80x9cpolyfunctionalxe2x80x9d compounds will give branching, which may be desirable in the polymer for polymer processing reasons. However too much of these polyfunctional compounds will lead to crosslinking. Crosslinking is undesirable for making thermoplastic (melt processible) polymer, but may be desired if a thermoset resin is the desired product.
Included within the meaning of the ingredients added to this process are any combinations of (other) ingredients which are known to react to give the needed ingredients in situ, such as the use of sulfur trioxide to dehydrate a carboxylic acid to its anhydride, as mentioned above.
As mentioned above, the byproduct carboxylic acid derived from the carboxylic acid anhydride may be recycled back into the process by being converted back to the carboxylic anhydride. A convenient way to do this is to react it with sulfur trioxide which acts as a dehydrating agent. Other methods known in the art for converting carboxylic acids to their anhydrides may be used xe2x80x9coutsidexe2x80x9d the polymerization process, and the xe2x80x9cregeneratedxe2x80x9d anhydride reused in the process. The carboxylic acid byproduct, if volatile enough, may be separated from the product polysulfone (and liquid medium, if any) by volatilization/distillate on.
The polymers produced by the process are useful as molding resins for various types of parts, such as parts that are heat and/or chemically resistant.
In the Examples the instrument used for MALDI had a time-of-flight detector and was a Vision(copyright) 2000 instrument made by ThermoBioanalysis located in Santa Fe, N. Mex., U.S.A.